Simultaneous multiplexed imaging system and method

ABSTRACT

A system and method for multiplexing multiple images of different colors using only a single spatial light modulator (SLM) are disclosed. In the disclosed system, a first dichroic beam splitter receives an image light of first and second wavelengths from the SLM, and reflects the image light of the first wavelength towards a first mirror and an image light of the second wavelength towards a second mirror. The first mirror reflects the image light of the first wavelength at a first angle, and the second mirror reflects the image light of the second wavelength at a second angle. Further, the system includes a second dichroic beam splitter that receives the image light of the first wavelength from the first mirror and the image light of the second wavelength from the second mirror, and recombines the image light of the first and second wavelengths to produce an overlap image.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional ApplicationSer. No. 61/878,729 filed on Sep. 17, 2013, and claims priority to U.S.Provisional Application Ser. No. 61/881,549, filed on Sep. 24, 2013,both of which are incorporated by reference herein in their entireties.

FIELD OF THE INVENTION

The present invention relates generally to a field of optics, and moreparticularly to an imaging system and method for producing a multiplexedimage.

BACKGROUND

Many industrial applications require two or more independent opticalimages of different wavelengths or colors to be simultaneously projectedonto the same specimen. As an example, in optogenetics research, a blueimage can be used to excite certain neurons while an orange or red imagecan be used to silence some other neurons.

In general, a spatial light modulator (“SLM”) may be used to generate animage to be projected onto a specimen. One conventional solution is touse multiple SLMs, where each generates an image of a single color, andthen combine the images into a single image. An example of such a systemis a three-panel color projector for display applications.

However, the use of a system having multiple SLMs has several drawbacks.Such system is expensive and requires a complex optical layoutarrangement. Also, it is not particularly suitable for applicationsrequiring a space-efficient compact design.

SUMMARY OF THE INVENTION

The present invention provides a solution to alleviate such problems.More particularly, the present invention provides systems and methods togenerate simultaneous multi-wavelength images utilizing a single SLM.

In one embodiment, an optical imaging system is provided. The opticalimaging system comprises a spatial light modulator (SLM) that receiveslight of a first wavelength and light of a second wavelength, andoutputs an image light of the first wavelength and an image light of thesecond wavelength, the first and second wavelengths being different fromeach other.

The optical imaging system further comprises (i) a first dichroic beamsplitter that receives the image light of the first and secondwavelengths from the SLM, and reflects the image light of the firstwavelength in a first direction and transmits the image light of thesecond wavelength in a second direction, (ii) a first mirror thatreceives the image light of the first wavelength from the first dichroicbeam splitter and reflects the image light of the first wavelength at afirst angle, (iii) a second mirror that receives the image light of thesecond wavelength from the first dichroic beam splitter and reflects thesecond wavelength at a second angle, and (iv) a second dichroic beamsplitter that receives the image light of the first wavelength from thefirst mirror and the image light of the second wavelength from thesecond mirror, and recombines the image light of the first and secondwavelengths to produce an overlap image.

In another embodiment, an optical imaging method is provided. In theoptical imaging method, a single spatial light modulator (SLM) is usedto produce an image having a first image half associated with a firstwavelength and a second image half associated with a second wavelength.The first image half is shifted in a first direction and the secondimage half is shifted in a second direction different from the firstdirection such that at least a portion of the first image half overlapsat least a portion of the second image half. The overlapped portions arethen output as an overlap image associated with the first and secondwavelengths.

Additional features and advantages of embodiments will be set forth inthe description, which follows, and in part will be apparent from thedescription. The objectives and other advantages of the invention willbe realized and attained by the structure particularly pointed out inthe example embodiments in the written description and claims hereof aswell as the appended drawings. It is to be understood that both theforegoing general description and the following detailed description areillustrative and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention are illustrated by way ofexample and are not limited to the following figures:

FIG. 1 illustrates an optical imaging system arranged in accordance withone embodiment of the present invention.

FIG. 2 is a flow chart showing an exemplary set of functions carried outusing the optical imaging system of FIG. 1.

FIG. 3A illustrates an example of an SLM image, in accordance with thepresent invention.

FIG. 3B illustrates an overlap between upper and lower halves of the SLMimage in accordance with the present invention.

FIG. 3C illustrates an overlap image, in accordance with the presentinvention.

FIG. 4 illustrates an example of an angular subtense in accordance withthe present invention.

FIG. 5 illustrates an optical imaging system arranged in accordance withanother embodiment of the present invention.

FIG. 6 is a flow chart showing an exemplary set of functions carried outusing the optical imaging system of FIG. 5.

DETAILED DESCRIPTION

Various embodiments and aspects of the invention will be described withreference to details discussed below, and the accompanying drawings willillustrate the various embodiments. The following description anddrawings are illustrative of the invention and are not to be construedas limiting the invention.

In this regard, different arrangements described herein are provided byway of example only, and other arrangements and elements can be added orused instead and some elements may be omitted altogether. Also, thoseskilled in the art will appreciate that many of the elements describedherein are functional entities that may be implemented as discretecomponents or in conjunction with other components, in any suitablecombination and location, and various functions could be carried out bysoftware, firmware and/or hardware.

Multiplex System

FIG. 1 depicts an optical imaging system 10 arranged in accordance withan illustrative embodiment of the present invention.

As shown in FIG. 1, the optical imaging system 10 comprises a lightsource 12 that may coupled to a single spatial light modulator (“SLM”)14 via a beam splitter and/or other optical components (not shown). Theoptical imaging system 10 further comprises a first lens 16 (alsoreferred to as “Lens A”), a first dichroic beam splitter 18 (alsoreferred to as “Dichroic 1”), a first mirror 20 (also referred to as“Mirror 1”), a second mirror 22 (also referred to as “Mirror 2”), asecond dichroic beam splitter 24 (also referred to as “Dichroic 2”), asecond lens 26 (also referred to as “Lens B”), and a field stop 28 (alsoreferred to as “Field stop”).

In accordance with the illustrative embodiment, the light source 12 isconfigured to illuminate the SLM 14 with light having different opticalproperties. In particular, in the illustrative embodiment, the lightsource 12 illuminates the SLM 14 with light of a first wavelength andlight of a second wavelength that is different from the firstwavelength. In the illustrative embodiment, the first wavelength is ashorter wavelength associated with a first color (e.g., a wavelength ofapproximately 450-495 nm corresponding to a blue color), while thesecond wavelength is a longer wavelength associated with a second color(e.g., a wavelength of approximately 620-740 nm corresponding a redcolor) different from the first color. Alternatively, the firstwavelength could be a longer wavelength, while the second wavelengthcould be a shorter wavelength. For the purpose of example, in FIG. 1,the light directed onto the SLM 14 is denoted as beams “A” and “B,”where the beam A corresponds to the light of the first wavelength andthe beam B corresponds to the light of the second wavelength.

The light source 12 may be any suitable one or more sources of light,such as LED(s) and/or solid-state laser device(s). For example, thelight source 12 may be a single light source capable of simultaneouslygenerating light of two or more different wavelengths (e.g., a whitelight source containing multiple wavelengths). Alternatively, the lightsource 12 may be multiple light sources each individually generatinglight of a given wavelength. Further, in the illustrative embodiment,the light from the light source 12 may pass through any suitable opticalcomponent(s).

To illustrate, the light source 12 may be two or more light sourcesproducing separate light beams with different wavelengths (e.g., a bluelight beam and a red light beam), and a beam combiner can be disposed inan illumination light path between the light source 12 and the SLM 14 tocombine those separate light beams and direct them onto the SLM 14.Those skilled in the art will appreciate that the beam combiner can be,e.g., a dichroic beam splitter that can separate multiple light beamsinto separate light beams of different wavelengths but can also beconfigured to function as a combiner to combine light beams of differentwavelengths.

In the illustrative embodiment, the first-wavelength light beam A andthe second-wavelength light beam B are directed onto the SLM 14 that, inturn, can modulate each wavelength independently. Preferably, the SLM 14is a digital micromirror device (“DMD”), as shown in FIG. 1. However, inother embodiments, the SLM 14 may be, for instance, in the form of aliquid crystal display (“LCD”) device including an imaging portion madeup of a pixel array.

As those skilled in the art will recognize, a typical DMD will include alarge number of microscopic mirrors that each represent an individualpixel and can be controlled to be either in an “on” state or an “off”state in accordance with binary data. The mirrors/pixels are arranged ina two-dimensional array of rows and columns, and the DMD can modulateincoming light in accordance with an image data to produce a desiredoutput image. Further, the dimensions of the pixel array will depend onthe resolution of the DMD (e.g., 1024 rows by 768 columns).

As a general matter, in accordance with the illustrative embodiment,light output by the SLM 14 will be then processed through the elements16-28 of the optical imaging system 10 to produce an overlap image basedon images of multiple different wavelengths or colors. The operation andremainder of the optical imaging system 10 will be now explained in moredetail with reference to a flow chart of FIG. 2 illustrating anexemplary set of functions carried out in the optical imaging system 10.

As shown in FIG. 2, at step 30, a user defines an image pattern Psassociated with the first wavelength and an image pattern Pl associatedwith the second wavelength. As noted above, in the illustrativeembodiment, the first wavelength is a shorter wavelength associated withthe first color, such as blue, and the second wavelength is a longerwavelength associated with the second color, such as red.

At step 32, the image pattern Ps is loaded to an upper half of the SLM14, and the image pattern Pl is loaded to a lower half of the SLM 14.Alternatively, the image pattern Pl may be loaded to the upper half ofthe SLM 14, and the image pattern Ps may be loaded to the lower half ofthe SLM 14. As used herein, the upper and lower halves of the SLM 14will refer respectively to upper and lower halves of a pixel array ofSLM 14 that produces an image, or a frame, output by the SLM 14.Further, the image pattern Ps represents first image data according towhich the SLM 14 will modulate light input to a half of the SLM 14loaded with the image pattern Ps to generate an image light in that halfof the SLM 14. On the other hand, the image pattern Pl represents secondimage data according to which the SLM 14 will modulate light input to ahalf of the SLM 14 loaded with the image pattern Pl to generate an imagelight in that half of the SLM 14. FIG. 3A shows an example of an SLMimage 50 output by the SLM 14, with the upper and lower halves of theSLM 14 denoted respectively.

Note that in the particular optical arrangement of FIG. 1, at the fieldstop 28, the image of the SLM 14 would be inverted, meaning that the SLMimage at the field stop 28 would be upside down and/or left-to-rightrelative to the original SLM image at the output of the SLM 14. However,to avoid confusion, throughout the present description, the phrases“upper half,” “lower half,” “shift up,” “shift down,” “shift left,” and“shift right” are always used with reference to the original image ofthe SLM 14, ignoring the image inverting property associated with theparticular optical arrangement illustrated in FIG. 1.

Although not shown, one skilled in the art will recognize that the SLM14, such as a DMD, will be configured with suitable hardware, processingunit(s), memory, software/logic modules, input lines, buses, and thelike, to process the image patterns Ps and Pl input into the SLM 14 andload them into appropriate portions of the pixel array of the SLM 14. Inthis regard, data represented by the image patterns can be loaded to thepixel array in any suitable fashion, such as on a row-by-row basis.

As shown in FIG. 3A, the SLM image 50 has an upper half 52 and a lowerhalf 54. As shown in FIG. 3A, the SLM image 50 has a two-dimensionalrectangular shape, with a width “w” and a height “h.” In accordance withthe illustrative embodiment, the upper half 52 of the SLM image 50corresponds to the upper half of the SLM 14, while the lower half 54 ofthe SLM image 50 corresponds to the lower half of the SLM 14.Accordingly, an image corresponding to the image pattern Ps associatedwith the first (shorter) wavelength will be generated in the upper half52 of the SLM image 50, while an image corresponding to the imagepattern Pl associated with the second (longer) wavelength will begenerated in the lower half 54 the SLM image 50.

As noted above, the light of the first wavelength and the light of thesecond wavelength from the light source 12 are illuminated onto the SLM14. Hence, referring back to FIG. 2, at step 34, the SLM 14 isilluminated with the light of the first wavelength and the light of thesecond wavelength. Note that, in the present embodiment, the whole SLM14 (or more specifically, the whole SLM pixel array) is illuminated withthe light of the first wavelength and the light of the secondwavelength. As such, the SLM 14 will modulate both the light of thefirst wavelength and the light of the second wavelength according to theimage patterns Ps and Pl to produce the SLM image 50. On the output ofthe SLM 14, the SLM image 50 will contain an image light associated withthe first wavelength and an image light associated with the secondwavelength.

At step 36, the first lens 16 projects the SLM image 50 to a certaindistance away from the SLM 14. In the illustrative embodiment, the firstlens 16 is a collimated lens that projects the SLM image 50 to infinity.However, in other embodiments, it may be possible to use a differenttype of lens or another optical component (e.g., a concave mirror). Aswill be described later, the second lens 26 refocuses the SLM 50 imageat a back focal plane of the lens 26. However, other conjugate lenspositions can be possible as well.

At step 38, the first dichroic beam splitter 18 separates the imagelight of the first wavelength and the image light of the secondwavelength. In the illustrative embodiment, the image light of the firstwavelength gets reflected in a first direction and the image light ofthe second wavelength gets transmitted in a second direction. As shownin FIG. 1, in this case, the image light of the first wavelength getsreflected upward towards the first mirror 20, while the image light ofthe second wavelength gets transmitted towards the second mirror 22.

In the illustrative embodiment, each of the mirrors 20 and 22 is tiltedat an angle θ (as indicated by the arrows in FIG. 1) relative to ahorizontal axis that passes though the center of the SLM 14 and thecenter of the first lens 16. The angle θ at which the mirrors 20 and 22are each tilted relative to the horizontal axis is such that the upperhalf 52 of the SLM image 50 and the lower half 54 of the SLM image 50will be centered along a final optical axis that passes through thecenter of the second lens 26 and the center of the field stop 28.

At step 40, the first mirror 20 tilted at the angle θ reflects the upperhalf 52 of the SLM image 50 to the center of the field stop 28, and thesecond mirror 22 tilted at the angle θ reflects the lower half 54 of theSLM image 50 to the center of the field stop 28. This causes a shift ofthe upper and lower halves 52 and 54 that results in an overlap betweenthe upper and lower halves 52 and 54 when the image light of the firstwavelength and the image light of the second wavelength are recombined.Namely, the SLM image 50 appearing at the first mirror 20 is shiftedspatially such that the upper half 52 of the SLM image 50 is shifteddownwards, while the SLM image 50 appearing at the second mirror 22 isshifted spatially such that the lower half 54 of the SLM image 50 isshifted upwards.

In the illustrative embodiment, the angle θ is given by the followingformula:

θ=45°+atan(w/(8*F _(a))), where

atan is arctangent,

w is a full width of the SLM image 50, and

F_(a) is a focal length of the first lens 16.

In the present disclosure, the width of the SLM image 50 is pictoriallydenoted in FIG. 3A. Further, note that, although the first lens 16projects the SLM image 50 to infinity, one skilled in the art wouldunderstand that such lens would have a finite focal length F_(a) used incalculating the angle θ.

Then, at step 42, the second dichroic beam splitter 24 recombines theimage light of the first wavelength and the image light of the secondwavelength to produce an overlap image. For example, in the illustrativeembodiment, the second dichroic beam splitter 24 is configured such thatthe image light of the first wavelength is transmitted and the imagelight of the second wavelength gets reflected. However, alternatively,the second dichroic beam splitter 24 may be configured such that theimage light of the second wavelength is transmitted and the image lightof the first wavelength gets reflected.

As noted above, the tilt of the first and second mirrors 20 and 22 atthe angle θ causes a shift of the upper and lower halves 52 and 54 whenthe image light of the first wavelength and the image light of thesecond wavelength are respectively reflected by those mirrors. Moreparticularly, the upper half 52 of the SLM image 50 is shifteddownwards, while the lower half 54 of the SLM image 50 is shiftedupwards. When the image lights are recombined, at the final image plane,the shift results in an overlapped portion 56 between the upper andlower halves 52 and 54 of the SLM image 50, as shown in FIG. 3B. In theillustrative embodiment, in the overlapped portion 56, thefirst-wavelength image of the upper half of the SLM image 50 and thesecond-wavelength image of the lower half of the SLM image 50 areprecisely overlaid.

At step 44, the second lens 26 projects the upper half 52 and the lowerhalf 54 of the SLM image 50 to the field stop 28 with the preciseoverlay. The field stop 28 may be, for example, a diaphragm that allowsa passage of light through its center aperture while blocking lightoutside of the aperture. However, other suitable forms of field stop maybe used as well.

Then, at step 46, the field stop 28 functions to block unwanted light sothat only an overlap image 58 appears at the final image plane, as shownin FIGS. 1 and 3C. As noted above, in the illustrative embodiment, thewhole SLM 14 is illuminated with the light of the first wavelength andthe light of the second wavelength. As such, the image light of thefirst wavelength would be present in the upper half 52 and the lowerhalf 54 of the SLM image 50. Similarly, the image light of the secondwavelength would be present in the upper half 52 and the lower half 54.After the wavelength separation at the first dichroic beam splitter 18,the SLM image 50 appearing at the first mirror 20 would contain only theimage light of the first wavelength (e.g., would appear as a blueimage), while the SLM image 50 appearing at the second mirror 22 wouldcontain only the image light of the second wavelength (e.g. would appearas a red image).

As such, as a result of the shift of the SLM image 50 downwards andupwards to overlap the upper half 52 and the lower half 54, a portion ofthe image light of the first wavelength originally present in the lowerhalf 54 of the SLM image 50 would still be present at the final imageplane in a lower SLM half, as shown in FIG. 3B. Similarly, a portion ofthe image light of the second wavelength originally present in the upperhalf 52 of the SLM image 50 would still be present at the final imageplane in an upper SLM half, as shown in FIG. 3B. Accordingly, the fieldstop 28 will block unwanted image light of the first wavelength from thelower SLM half, and will block unwanted image light of the secondwavelength from the upper SLM half so that only image lightcorresponding to the overlapped portion 56 passes through the field stop28, resulting in the overlap image 58. In the illustrative embodiment,the angle θ is set such that the overlap image 58 is about half of thesize of the SLM image 50, namely about half the width “w” of the SLMimage 50, as shown in FIGS. 3B and 3C. Hence, the aperture of the fieldstop 28 could be set to the width of the overlap image 58 (e.g., w/2) tolet through only the overlap image 58 and block other light. Note that,in other embodiments, it is possible to adjust the angle θ to obtain asmaller degree of overlap between the upper and lower halves 52 and 54if one does not wish to fully utilize the entire half of the pixel arrayof the SLM 14. In this case, the size of the aperture of the field stop28 could be set accordingly to let through only the portion of overlap.

As described above, at the final image plane, the first-wavelength imagefrom the upper half of the SLM 14 and the second-wavelength image fromthe lower half of the SLM 14 can be merged and precisely overlay eachother. As a result, each pixel in the overlap image 58 corresponds totwo physically different pixels on the SLM 14 and can be controlled bythose two pixels simultaneously: one pixel from the upper half of theSLM 14 and one pixel from the lower half of the SLM 14. As describedabove, in the present embodiment, the image pattern Ps associated withthe first wavelength is loaded to the upper half of the SLM 14, whilethe image pattern Pl associated with the second wavelength is loaded tothe lower half of the SLM 14. This way, the upper half of the SLM 14controls the first wavelength and the lower half of the SLM 14 controlsthe second wavelength.

To illustrate, FIG. 3A shows a pixel 60 in the upper half 52 of the SLMimage 50 and a pixel 62 in the lower half 54 of the SLM image 50. As setforth above, the upper half 52 of the SLM image 50 corresponds to theupper half of the SLM 14, while the lower half 54 of the SLM image 50corresponds to the lower half of the SLM 14. Therefore, when the upperhalf 52 is shifted downwards and the lower half 54 is shifted upwardssuch that those image halves are overlaying each other, a pixel 64 inthe overlap image 58 will correspond to an overlap between the pixels 60and 62. The pixel 60 corresponds to a pixel of the first color from theupper half of the SLM 14 (e.g., a first row of the upper half of thepixel array of the SLM 14) and the pixel 62 corresponds to a pixel ofthe second color from the lower half of the SLM 14 (e.g., a first row ofthe lower half of the pixel array of the SLM 14).

As such, since the pixels 60 and 62 are physically two different pixelson the SLM 14, the pixel 64 in the overlap image 58 can be controlled byturning the pixels 60 and 62 on and off on the side of SLM 14. Since thepixels 60 and 62 correspond to physically separate pixels on the SLM 14,they can be turned on and off independent of each other. Hence, thepixel 62 can emit either light associated with the first wavelength(e.g., blue color) or light associated with the second wavelength (e.g.,red color), or a mixture of both wavelengths.

Advantageously, in the illustrative embodiment, it is possible tomultiplex simultaneous images utilizing only a single SLM to produce aspatially overlaid image of multiple independent colors, such as theoverlap image 58. This can have many important applications, such as inmicroscopy.

To illustrate, projecting simultaneously multiplexed images from asingle SLM through a microscope onto a specimen is a powerful tool inapplications such as fluorescence microscopy, photoactivation,optogenetics, structured illumination, and others. With a benefit of thepresent embodiment, one can simultaneously illuminate certain portionsof a specimen with light of one color and other portions of the specimenwith a light of another color using only a single SLM.

In this regard, the image patterns Ps and Pl can be configured such thatwhen the images of the first and second colors in the upper and lowerhalves 52 and 54 are overlapped, the overlap image 58 contains desiredimage shapes for each color (e.g., a red circle and a blue triangle).However, since each pixel in the overlap image 58 can be controlledindependently using pixels of multiple different colors on the SLM side,it is possible to create desired color images in the overlap image 58 byselectively controlling individual pixels on the SLM 14. For example,one can modify the initially loaded image pattern or load a new imagepattern to change an image of a given color as desired or selectivelyturn that image on and off, etc.

Note that in the illustrative embodiment, the two mirrors 20 and 22 andthe two dichroic beam splitters 18 and 24 are arranged so that not onlyare images of the two wavelengths overlaid precisely at the final imageplane, but also exit pupils of the two images are precisely overlaid ontop of each other. More specifically, in the system arrangement of FIG.1, both exit pupils are at infinity. This is an important feature formicroscopy where an exit pupil of a projection system will be imaged atan entrance pupil of the microscope objective in order to maximize lightthroughput for both wavelengths.

Further, although FIG. 1 shows one illustrative embodiment of theoptical imaging system 10, variations are possible.

For example, although in the above description the terms “firstwavelength” and “second wavelength” are used respectively in referenceto single wavelengths (e.g., a wavelength associated with a particularcolor (e.g., red or blue)), it should be understood that each of theseterms can also represent a band of wavelengths rather than a singlewavelength. To illustrate, in one alternative embodiment, the firstwavelength can represent a first band of wavelengths, while the secondwavelength can represent a second band of wavelengths different from thefirst band of wavelengths.

Further, although the above description describes an embodiment in whichthe upper and lower halves of the SLM 14 are being used, in analternative embodiment, it is also possible to configure the opticalimaging system 10 to use right and left halves of the SLM 14 instead,with the left and right halves referring respectively to left and righthalves of the pixel array of SLM 14. In this case, two SLM image halveswould be shifted respectively in a leftward direction and a rightwarddirection to overlap them. One skilled in the art will recognize thatthe angle θ may be adjusted accordingly to generate such shift.

Further, in one alternative embodiment, the first lens 16 may be omittedfrom the optical imaging system 10. Similarly, the second lens 26 may beomitted as well. Since the first lens 16 would no longer be a part ofthe system, the angle θ at which the first and second mirrors 20 and 22are tilted can be generalized as follows:

θ=45°+((⅛)*(angular subtense of an incoming SLM image)), where

the incoming SLM image is the SLM image 50 as viewed at a position ofthe first dichroic beam splitter 18.

As known in the art, an angular subtense generally refers to an anglesubtended by a source at a point of measurement. In the present case,the angular subtense of the incoming SLM image would thus generallyrefer to an angle subtended by the SLM image 50 as viewed from the firstdichroic beam splitter 18 positioned at a certain distance “d” away fromthe SLM 14. The subtended angle may be determined by measuring orcalculating an angle whose rays pass through the endpoints of the SLMimage 50, as pictorially depicted in FIG. 4.

One should also note that the system arrangement shown in FIG. 1 canalso be used for multiplexing optical properties other than awavelength. For example, in one alternative embodiment, if the dichroicbeam splitters are replaced by polarization beam splitters, then it ispossible to multiplex two images with different polarizations together.Practically, in this embodiment, for the polarization multiplexing towork optimally, it is more suitable to have the lower half of the SLM 14to pass through a polarization beam splitter that would replace thesecond dichroic beam splitter 24, and the upper half of the SLM 14 to bereflected by the same polarization beam splitter.

In yet another alternative embodiment, it is possible to add additionalstage(s) of dichroic beam splitters and mirrors so that one cangenerate, for example, a four-wavelength image by using a single SLM.For example, the SLM 14 can be divided into four quadrants, with eachquadrant responsible for one wavelength. The light source 12 can beconfigured to provide light of four different wavelengths. The firststage will shift the image quadrants up and down in a similar fashion asdescribed in connection with the arrangement of FIG. 1. The secondstage, on the other hand, will shift an image at the output of the firststage left and right so that at the end of the second stage, one willhave a final image having a size of a single quadrant. Each pixel in thefinal image corresponds to four physically different pixels in the SLMarray. Modulation of each of the four physical pixels allows for acontrol of four different wavelengths in the final image.

As noted above, in the illustrative embodiment, the whole SLM 14 isilluminated with the light of the first wavelength and the light of thesecond wavelength. However, in another embodiment, one can arrange tohave the upper half of the SLM 14 illuminated only with the light of thefirst wavelength, and the lower half of the SLM 14 illuminated only withthe light of the second wavelength. In this case, the image light of thefirst wavelength would be present only in the upper half 52 of the SLMimage 50 and the image light of the second wavelength would be presentonly in the lower half 54 of the SLM image 50. Hence, after thewavelength separation at the first dichroic beam splitter 18, the lowerhalf 54 of the SLM image 50 appearing at the first mirror 20 would bedark, and the upper half 52 of the SLM image 50 appearing at the secondmirror 22 would also be dark. After the image shift, the upper and lowerhalves 52 and 54 would be precisely overlaid. However, unlike in thescenerio shown in FIG. 3B, other portions of the SLM image 50 would bedark since each half of the SLM array was only illuminated with light ofone given wavelength.

As a result, one would not need the field stop 28 at the final imageplane. Furthermore, in this case, the dichroics may be replaced byneutral beamsplitters (e.g., partial mirrors) if optical efficiency isnot a great concern.

Multiplex System with a Fiber Array

FIG. 5 shows an optical imaging system 70, which is a modified versionof the optical imaging system 10 of FIG. 1, in accordance with anotherembodiment. As shown in FIG. 4, the optical imaging system 70 isidentical to the optical imaging system 10, except for an addition of afiber array 72 coupled on the output of the field stop 28 at the finalimage plane at which the overlap image 58 is produced. In turn, FIG. 6is a flow chart illustrating an exemplary set of functions carried outin the optical imaging system 70 in accordance with the this embodiment.

In the present embodiment, the fiber array 72 is a furcated fiber bundlemade up of multiple individual optical fibers through which light can betransmitted. In one example, such fiber array may be formed by bundlingoptical fibers, and polishing their ends. The fiber array 72 may becoupled onto the output of the field stop 28 directly (e.g., by placingthe fiber array 72 at the output of the field stop 28) or by means ofany suitable optical component(s) to direct light coming out of thefield stop 28 into the fiber array 72.

As shown in FIG. 6, the set of functions 80-96 is the same as the set offunctions 30-46 shown in FIG. 2. Therefore, the description of thosesteps will not be repeated here. However, in the system arrangement ofFIG. 5, at step 98, a front facet (or a common end) of the fiber array72 is placed at the final image plane (or the field stop 28) so thatlight is coupled into the fiber array 72. As such, the overlap image 58is projected onto a front facet (or a common end) of the fiber array 72.

Accordingly, pixels on the SLM 14 corresponding to pixels within theoverlap image 58 may be precisely mapped to individual fibers in thefiber array 72. As discussed above, each pixel in the overlap image 58corresponds to multiple physically different pixels in the array of theSLM 14. Hence, in one example, the fiber array 72 may be configured suchthat each individual optical fiber corresponds to each pixel in theoverlap image 58, and hence two physically different pixels on the SLM14. Alternatively, it may be possible to configure the fiber array 72such that each individual optical fiber corresponds to multiple pixelsin the overlap image 58, and hence to more than two physically differentpixels on the SLM 14.

Advantageously, with the present embodiment, light in each individualoptical fiber of the fiber array 72 can be independently modulated bythe SLM 14. This results in a fiber array light source with multipleindividually-controlled light outputs that each can produce light ofmultiple wavelengths.

The present embodiment can be beneficially applied in differentapplications that use fiber array light sources. For example, inoptogenetics, it may be desirable to stimulate some specimens innumerous different places (e.g., 20 or even 100 different places).Coupling an individual light source into each optical fiber of suchlight source is highly impractical. With a benefit of the presentembodiment, only a limited number of light sources illuminating the DMDis needed to get a desired light out of each optical fiber of the fiberarray 72. Each optical fiber may be controlled by particular pixels onthe SLM 14. Those pixels can be selectively turned on and off in orderto control whether light of one or more of multiple wavelengths is sentthrough that fiber or not.

In another example, in optogenetics research, each individual opticalfiber of the fiber array 72 can be inserted into a different part of abrain in order to activate and silence different parts of the brain. Theavailability of two or more simultaneous wavelengths enables researchersto have fully independent control of the activating and silencingpatterns.

Additionally, one unique feature of the fiber array light source of thepresent embodiment is that light transmission rate in each fiber can betrimmed by turning a certain number of pixels off. For example, if anoptical fiber is covered by 10 pixels, then turning one of the pixelsoff results in a 10% reduction of the light intensity in the opticalfiber. This mechanism differs from the pulse-width modulation (PWM)employed in the operation of micromirror devices. PWM causes intensityfluctuations, but the intensity trimming features described above keep aconstant light intensity.

Note that, as in the case of the arrangement of FIG. 1, variations arepossible. In this regard, various modifications and alternativeembodiments discussed above with respect to the optical imaging system10 could equally apply to the optical imaging system 70.

As used herein, any reference to “one embodiment” or “an embodiment”means that a particular element, feature, structure, or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. The appearances of the phrase “in one embodiment” in variousplaces in the specification are not necessarily all referring to thesame embodiment.

Some embodiments may be described using the expression “coupled” and“connected” along with their derivatives. It should be understood thatthese terms are not intended as synonyms for each other. For example,some embodiments may be described using the term “connected” to indicatethat two or more elements are in direct physical or electrical contactwith each other. In another example, some embodiments may be describedusing the term “coupled” to indicate that two or more elements are indirect physical or electrical contact. The term “coupled,” however, mayalso mean that two or more elements are not in direct contact with eachother, but yet still co-operate or interact with each other. Theembodiments are not limited in this context.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive or and not to an exclusive or. For example,a condition A or B are satisfied by any one of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

The terms “a” or “an,” as used herein, are defined as one or more thanone. The term “plurality,” as used herein, is defined as two or morethan two. The term “another,” as used herein, is defined as at least asecond or more.

The invention can be implemented in numerous ways, including as aprocess, an apparatus, and a system. In this specification, theseimplementations, or any other form that the invention may take, may bereferred to as techniques. In general, the order of the connections ofdisclosed apparatus may be altered within the scope of the invention.

The present invention has been described in particular detail withrespect to some possible embodiments. Those skilled in the art willappreciate that the invention may be practiced in other embodiments.First, the particular naming of the components, capitalization of terms,the attributes, data structures, or any other programming or structuralaspect is not mandatory or significant, and the mechanisms thatimplement the invention or its features may have different names,formats, or protocols. Further, the system may be implemented via acombination of hardware and software, as described, or entirely inhardware elements. Also, the particular division of functionalitybetween the various system components described herein is merelyexemplary, and not mandatory; functions performed by a single systemcomponent may instead be performed by multiple components, and functionsperformed by multiple components may instead be performed by a singlecomponent. An ordinary artisan should require no additional explanationin developing the methods and systems described herein but maynevertheless find some possibly helpful guidance in the preparation ofthese methods and systems by examining standard reference works in therelevant art.

These and other changes can be made to the invention in light of theabove detailed description. In general, in the following claims, theterms used should not be construed to limit the invention to thespecific embodiments disclosed in the specification and the claims, butshould be construed to include all methods and systems that operateunder the claims set forth herein below. Accordingly, the invention isnot limited by the invention, but instead its scope is to be determinedentirely by the following claims.

What is claimed is:
 1. An optical imaging system, comprising: a spatiallight modulator (SLM) that receives light of a first wavelength andlight of a second wavelength, and outputs an image light of the firstwavelength and an image light of the second wavelength, the first andsecond wavelengths being different from each other; a first dichroicbeam splitter that receives the image light of the first and secondwavelengths from the SLM, and reflects the image light of the firstwavelength in a first direction and transmits the image light of thesecond wavelength in a second direction; a first mirror that receivesthe image light of the first wavelength from the first dichroic beamsplitter and reflects the image light of the first wavelength at a firstangle; a second mirror that receives the image light of the secondwavelength from the first dichroic beam splitter and reflects the imagelight of the second wavelength at a second angle; and a second dichroicbeam splitter that receives the image light of the first wavelength fromthe first mirror and the image light of the second wavelength from thesecond mirror, and recombines the image light of the first and secondwavelengths to produce an overlap image.
 2. The optical imaging systemof claim 1, wherein the first wavelength is associated with a firstcolor and the second wavelength is associated with a second color. 3.The optical imaging system of claim 1, wherein the first wavelength is ashorter wavelength and the second wavelength is a longer wavelength. 4.The optical imaging system of claim 1, wherein the first wavelength is alonger wavelength and the second wavelength is a shorter wavelength. 5.The optical imaging system of claim 1, wherein: the SLM comprises afirst half and a second half; in the overlap image, the first half ofthe SLM controls the image light of the first wavelength; and in theoverlap image, the second half of the SLM controls the image light ofthe second wavelength.
 6. The optical imaging system of claim 5,wherein: the first half is an upper half; and the second half is a lowerhalf.
 7. The optical imaging system of claim 5, wherein: the first halfcorresponds to a first half of a pixel array of the SLM; and the secondhalf corresponds to a second half of the pixel array of the SLM.
 8. Theoptical imaging system of claim 1, wherein: the SLM comprises an upperhalf and a lower half; the upper half is loaded with a first imagepattern, the first image pattern being associated with the firstwavelength; and the lower half is loaded with a second image pattern,the second image pattern being associated with the second wavelength. 9.The optical imaging system of claim 8, wherein: the upper halfcorresponds to an upper half of a pixel array of the SLM; and the lowerhalf corresponds to a lower half of the pixel array of the SLM.
 10. Theoptical imaging system of claim 8, wherein the first image pattern isassociated with an image of a first color, and the second image patternis associated with an image of a second color.
 11. The optical imagingsystem of claim 10, wherein the first color is blue, and the secondcolor is red.
 12. The optical imaging system of claim 1, wherein animage output by the SLM corresponds to a frame of the SLM.
 13. Theoptical imaging system of claim 1, wherein to recombine the image lightof the first and second wavelengths, the second beam splitter (i)reflects the image light of the first wavelength and transmits the imagelight of the second wavelength, or (ii) reflects the image light of thesecond wavelength and transmits the image light of the first wavelength.14. The optical imaging system of claim 1, wherein the overlap imagecomprises an upper image half associated the first wavelength and alower image half associated with the second wavelength, the two imagehalves overlapping each other.
 15. The optical imaging system of claim14, wherein the first wavelength is a shorter wavelength and the secondwavelength is a longer wavelength.
 16. The optical imaging system ofclaim 1, wherein the overlap image comprises a right image halfassociated with the first wavelength and a left image half associatedwith the second wavelength, the two halves overlapping each other. 17.The optical imaging system of claim 1, wherein: the SLM modulates thelight of the first wavelength to produce the image light of the firstwavelength; and the SLM modulates the light of the second wavelength toproduce the image light of the second wavelength.
 18. The opticalimaging system of claim 1, wherein the first angle and the second angleare calculated according to the following formula:θ=45°+((⅛)*(angular subtense of an incoming SLM image)), where, theincoming SLM image is an SLM image as viewed at a position of the firstdichroic beam splitter.
 19. The optical imaging system of claim 1,further comprising a first lens, coupled between the SLM and the firstdichroic beam splitter, that receives the image light of the firstwavelength and the image light of the second wavelength from the SLM,and that projects the image light of the first and second wavelengthsfor a specified distance.
 20. The optical imaging system of claim 19,wherein the first angle and the second angle are calculated according tothe following formula:θ=45°+atan(w/(8*F _(a))), where atan is arctangent, w is a width of anSLM image, and F_(a) is a focal length of the first lens.
 21. Theoptical imaging system of claim 1, further comprising: a field stop; anda second lens that receives the recombined image light of the first andsecond wavelengths from the second dichroic beam splitter, and forms anoutput image of the SLM at the field stop.
 22. The optical imagingsystem of claim 1, wherein each pixel in the overlap image correspondsto two physically different pixels on the SLM.
 23. The optical imagingsystem of claim 1, wherein the whole SLM is illuminated with both thelight of the first and the light of the second wavelength.
 24. Theoptical imaging system of claim 1, wherein: the SLM comprises a firsthalf and a second half; the first half of the SLM is illuminated withthe light of the first wavelength; and the second half of the SLM isilluminated with the light of the second wavelength.
 25. The opticalimaging method, comprising: using a single spatial light modulator (SLM)to produce an image having a first image half associated with a firstwavelength and a second image half associated with a second wavelength,shifting the first image half in a first second direction and shiftingthe second image half in a second direction different from the firstdirection such that at least a portion of the first image half overlapsat least a portion of the second image half; and outputting theoverlapped portions as an overlap image associated with the first andsecond wavelengths.
 26. The optical imaging method of claim 25, whereinthe first direction is an downward direction and the second direction isan upward direction.
 27. The optical imaging method of claim 25, whereinthe first direction is a leftward direction and the second direction isa rightward direction.
 28. The optical imaging method of claim 25,wherein: the first image half is shifted in the first direction and thesecond image half is shifted in the second direction such that the firstimage half and the second image half overlay each other.
 29. The opticalimaging method of claim 25, wherein the first wavelength is associatedwith a first color and the second wavelength is associated with a secondcolor.
 30. The optical imaging method of claim 25, wherein: shifting thefirst image half comprises reflecting an image light of the firstwavelength output by the SLM at a first angle using a first mirror; andshifting the second image half comprises reflecting an image light ofthe second wavelength output by the SLM at a second angle using a secondmirror.
 31. The optical imaging method of claim 25, wherein each pixelin the overlap image corresponds to two physically different pixels onthe SLM.
 32. The optical imaging method, comprising: using a singlespatial light modulator (SLM) to produce an image having a first imagequadrant associated with a first wavelength, a second image quadrantassociated with a second wavelength, a third image quadrant associatedwith a third wavelength, and a fourth image quadrant associated with afourth wavelength, the four wavelengths being different from each other;shifting respective image quadrants up and down to produce a firstoverlap image; and shifting the first overlap image left and right toproduce a second overlap image having a size of one image quadrant. 33.The optical imaging method of claim 32, wherein each pixel in the secondoverlap image corresponds to four physically different pixels on theSLM.